|SINGH, SHARDENDU - University Of Maryland Eastern Shore (UMES)|
Submitted to: Photochemistry and Photobiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2015
Publication Date: 8/19/2015
Citation: Singh, S.K., Reddy, V. 2015. Response of carbon assimilation and chlorophyll fluorescence to soybean leaf phosphorus across CO2: Alternative electron sink, nutrient efficiency and critical phosphorus concentration. Photochemistry and Photobiology. 151:276-284.
Interpretive Summary: Phosphorus is an important limiting factor for crop growth and development in many soil types worldwide. It is a major plant nutrient and essential for plant photosynthesis. The atmospheric carbon dioxide (CO2) is projected to double from the current level of 400 ppm by the end of 21st century. Generally, high CO2 increases plant photosynthesis and growth. However, the availability of phosphorus in soil limits the overall beneficial effect of high CO2. Results showed a severe decline in the degree of photosynthetic stimulation by high CO2 under phosphorus deficiency. Plants grown under high CO2 needed more phosphorus to achieve maximum photosynthesis capacity as compared to the current level of CO2. The results will be of interest among researchers and agronomists attempting to enhance crop photosynthesis under stress conditions such as in phosphorus-deficient soils at current and future atmospheric carbon dioxide concentration.
Technical Abstract: To evaluate the response of CO2 assimilation (PN) and various chlorophyll fluorescence (CF) parameters to phosphorus (P) nutrition soybean plants were grown in controlled environment growth chambers with sufficient (0.50 mM) and deficient (0.10 and 0.01 mM) P supply under ambient and elevated CO2 (aCO2, 400 and eCO2, 800 µmol mol-1, respectively). Measurements were made under normal (21%) and low (2%) O2 concentrations. A significant P × CO2 interaction was not observed for PN and CF parameters. Results showed a strong correlation between leaf tissue P concentration with PN and CF parameters regardless of CO2 and O2 concentrations. A simultaneous decrease in PN, quantum efficiency (Fv’/Fm’), quantum yield of photosystem II (PhiPSII) and CO2 fixation (PhiCO2), and photochemical quenching (qP) was observed under P deficiency. The Fv’/Fm’ decreased as a result of greater decline in maximal (Fm’) than minimal (Fo’) fluorescence yields. Elevated CO2 stimulated PN and increased PhiCO2 especially under higher leaf P concentration. The 2% O2 also stimulated PN and PhiCO2 but only at aCO2. Moreover, the degree of PN stimulation by eCO2 was reduced with leaf P concentration showing higher sensitivity of PN to P deficiency under eCO2. Overall, CF parameters exhibited greater sensitivity to P nutrition than to either CO2 or O2. Photoinhibition and occurrence of excess energy dissipation by non-photochemical quenching or non-radiative mechanisms was suggested under both the eCO2 and the 2% O2 concentrations. An increased phosphorus utilization efficiency of PN and CF parameters was also achieved, but with the expense of net CO2 assimilation in P-deficient leaves. The results showed that the critical leaf P concentration (CLPC) needed to achieve 90% of the maximum PN and PhiCO2 was greater than CF parameters. Moreover, the CLPC was always higher at eCO2 versus aCO2. Thus, eCO2 is likely to increase CLPC for photosynthetic processes in soybean suggesting increased sensitivity of soybean to P deficiency under eCO2.